We present a study on the structure of quiescent filament channels observed by Hinode/XRT and STE... more We present a study on the structure of quiescent filament channels observed by Hinode/XRT and STEREO/EUVI from December 2006 to February 2009. For 10 channels identified on the solar disk, we find that the emission on the two sides of the channel is asymmetric in both X-rays and EUV: one side has curved bright features while the other side has straight faint features. We interpret the results in terms of a magnetic flux rope model. The asymmetry in the emission is due to the variation in axial magnetic flux along the channel, which causes one polarity to turn into the flux rope, while the field lines from the other polarity are open or connected to very distant sources. For 70 channels identified by cavities at the limb, the asymmetry cannot be clearly identified.
Observing the Sun at high time and spatial scales is a step toward understanding the finest and f... more Observing the Sun at high time and spatial scales is a step toward understanding the finest and fundamental scales of heating events in the solar corona. The high-resolution coronal (Hi-C) instrument has provided the highest spatial and temporal resolution images of the solar corona in the EUV wavelength range to date. Hi-C observed an active region on 2012 July 11 that exhibits several interesting features in the EUV line at 193 A. One of them is the existence of short, small brightenings "sparkling" at the edge of the active region; we call these EUV bright dots (EBDs). Individual EBDs have a characteristic duration of 25 s with a characteristic length of 680 km. These brightenings are not fully resolved by the SDO/AIA instrument at the same wavelength; however, they can be identified with respect to the Hi-C location of the EBDs. In addition, EBDs are seen in other chromospheric/coronal channels of SDO/AIA, which suggests a temperature between 0.5 and 1.5 MK. Based on t...
The second Hi-C flight (Hi-C2.1) provided unprecedentedly-high spatial and temporal resolution (∼... more The second Hi-C flight (Hi-C2.1) provided unprecedentedly-high spatial and temporal resolution (∼250km, 4.4s) coronal EUV images of Fe IX/X emission at 172Å, of AR 12712 on 29-May-2018, during 18:56:21-19:01:56 UT. Three morphologically-different types (I: dot-like, II: loop-like, III: surge/jetlike) of fine-scale sudden-brightening events (tiny microflares) are seen within and at the ends of an arch filament system in the core of the AR. Although type Is (not reported before) resemble IRIS-bombs (in size, and brightness wrt surroundings), our dot-like events are apparently much hotter, and shorter in span (70s). We complement the 5-minute-duration Hi-C2.1 data with SDO/HMI magnetograms, SDO/AIA EUV images, and IRIS UV spectra and slit-jaw images to examine, at the sites of these events, brightenings and flows in the transition-region and corona and evolution of magnetic flux in the photosphere. Most, if not all, of the events are seated at sites of opposite-polarity magnetic flux convergence (sometimes driven by adjacent flux emergence), implying likely flux cancellation at the microflare's polarity inversion line. In the IRIS spectra and images, we find confirming evidence of field-aligned outflow from brightenings at the ends of loops of the arch filament system. In types I and II the explosion is confined, while in type III the explosion is ejective and drives jet-like outflow. The light-curves from Hi-C, AIA and IRIS peak nearly simultaneously for many of these events and none of the events display a systematic cooling sequence as seen in typical coronal flares, suggesting that these tiny brightening-events have chromospheric/transition-region origin.
Symposium - International Astronomical Union, 1980
The soft x-ray (2–54 Å) pictures obtained by the S-054 experiment aboard SKYLAB provide an excell... more The soft x-ray (2–54 Å) pictures obtained by the S-054 experiment aboard SKYLAB provide an excellent opportunity to study the association of x-ray loop structures with radio bursts. We report here on the properties of meter-decameter wavelength radio bursts which appear to be associated with two different types of loop structures: a)Relatively short lived small scale loops, which are observed to link magnetic fields of opposite polarity, called x-ray bright points (XBPs); andb)Longer lived loop systems which appear to connect opposite magnetic polarities of an active region and active region complexes as well.
Soft X-ray images of the solar corona obtained during the last 20 years have systematically shown... more Soft X-ray images of the solar corona obtained during the last 20 years have systematically shown an intimate relationship between intense emitting structures and magnetic fields (Vaiana and Rosner 1978). The magnetic field confines a 106 K plasma, which is an intense source of soft X-ray photons. Therefore, it is natural to expect the bright X-ray structures to follow the field’s geometry. But this relationship does not seem to be just geometrical. It is generally believed that the energy necessary to heat the plasma comes from the dissipation of magnetic stresses, which are continually being re-generated by subphotospheric convective motions. However, there is still great uncertainty about the precise physical mechanisms involved in the production and release of the magnetic energy.
Proceedings of the International Astronomical Union, 2006
We present a statistical investigation of shear motion of the EUV footpoints in tworibbon solar f... more We present a statistical investigation of shear motion of the EUV footpoints in tworibbon solar flares, using the high spatial resolution data obtained in 1998-2005 by the Transition Region and Coronal Explorer (TRACE). In this study we have selected 50 well-observed X-and M-class two-ribbon flares. Our preliminary results are: a) 86% (43 out of 50) of these flares show shear change of footpoints and ribbon separation; b) there is no obvious ribbon separation in those 7 flares which have no shear change of the conjugate footpoints; c) in most events, the cessation of shear change is 0-2 minutes earlier than the end of the impulsive phase.
the Earth's force, needed to be taken into account from the start. In important ways, d' ... more the Earth's force, needed to be taken into account from the start. In important ways, d' Alembert was an inventive and insightful investigator in the areas of continuum mechanics and celestial mechanics, during the dozen or so years of his intense investment of himself in these studies. But he was a poor expositor, and his ideas also present intrinsic difficulties. Students seeking to assess his contributions to celestial mechanics must be immensely grateful to Dr ChaprontTouze for bringing the early memoirs into print and facilitating in innumerable ways our access to them.
Observations made with the Normal Incidence X-ray Telescope (NIXT) have shown that some X-ray emi... more Observations made with the Normal Incidence X-ray Telescope (NIXT) have shown that some X-ray emitting structures observed with NIXT resemble very closely the corresponding H-alpha plages. We have used hydrostatic models of coronal loops to explain such observations as strong emission from the lower section of high-pressure coronal arches.
Solar soft X-ray images taken simultaneously by the Yohkoh and the Normal Incidence X-ray Telesco... more Solar soft X-ray images taken simultaneously by the Yohkoh and the Normal Incidence X-ray Telescope (NIXT) reveal significantly different coronal structures. Coronal loops are more clearly seen in the Yohkoh images, and the isolated island-like structures seen in the NIXT image have been found to correspond to the footpoints of the Yohkoh loops. The difference is due to the difference in the temperature response of the telescopes: NIXT is sensitive to temperatures ranging from 0.9 to 3 MK, while Yohkoh is more sensitive to temperatures above 2.5 MK. The morphological differences reflect the multi-temperature (1-5 MK) nature of the solar coronal plasmas.
During the past year we have completed the changeover from the NIXT program to the new TXI soundi... more During the past year we have completed the changeover from the NIXT program to the new TXI sounding rocket program. The NIXT effort, aimed at evaluating the viability of the remaining portions of the NIXT hardware and design, has been finished and the portions of the NIXT which are viable and flightworthy, such as filters, mirror mounting hardware, electronics and telemetry interface systems, are now part of the new rocket payload. The backup NIXT multilayer-coated x-ray telescope and its mounting hardware have been completely fabricated and are being stored for possible future use in the TXI rocket. The H-alpha camera design is being utilized in the TXI program for real-time pointing verification and control via telemetry. A new H-alpha camera has been built, with a high-resolution RS170 CCD camera output. Two papers, summarizing scientific results from the NIXT rocket program, have been written and published this year: 1. "The Solar X-ray Corona," by L. Golub, Astrophysics and Space Science, 237, 33 (1996). 2. "Difficulties in Observing Coronal Structure," Keynote Paper, Proceedings STEPWG1 Workshop on Measurements and Analyses of the Solar 3D Magnetic Field, Solar Physics, 174, 99 (1997).
The postflight performance evaluation of the X-ray telescope was summarized. All payload systems ... more The postflight performance evaluation of the X-ray telescope was summarized. All payload systems and subsystems performed well within acceptable limits, with the sole exception of the light-blocking prefilters. Launch, flight and recovery were performed in a fully satisfactory manner. The payload was recovered in a timely manner and in excellent condition. The prefilter performance analysis showed that no X-ray images were detected on the processed flight film. Recommendations for improved performance are listed.
The coronal heating problem remains unsolved today, 80 years after its discovery, despite 50 year... more The coronal heating problem remains unsolved today, 80 years after its discovery, despite 50 years of suborbital and orbital coronal observatories. Tens of theoretical coronal heating mechanisms have been suggested, but only a few have been able to be ruled out. In this talk, we will explore the reasons for the slow progress and discuss the measurements that will be needed for potential breakthrough, including imaging the solar corona at small spatial scales, measuring the chromospheric magnetic fields, and detecting the presence of high temperature, low emission measure plasma. We will discuss three sounding rocket instruments developed to make these measurements: the High resolution Resolution Coronal Imager (Hi-C), the Chromospheric Lyman-Alpha Spectropolarimeter (CLASP), and the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS).
We present a study on the structure of quiescent filament channels observed by Hinode/XRT and STE... more We present a study on the structure of quiescent filament channels observed by Hinode/XRT and STEREO/EUVI from December 2006 to February 2009. For 10 channels identified on the solar disk, we find that the emission on the two sides of the channel is asymmetric in both X-rays and EUV: one side has curved bright features while the other side has straight faint features. We interpret the results in terms of a magnetic flux rope model. The asymmetry in the emission is due to the variation in axial magnetic flux along the channel, which causes one polarity to turn into the flux rope, while the field lines from the other polarity are open or connected to very distant sources. For 70 channels identified by cavities at the limb, the asymmetry cannot be clearly identified.
Observing the Sun at high time and spatial scales is a step toward understanding the finest and f... more Observing the Sun at high time and spatial scales is a step toward understanding the finest and fundamental scales of heating events in the solar corona. The high-resolution coronal (Hi-C) instrument has provided the highest spatial and temporal resolution images of the solar corona in the EUV wavelength range to date. Hi-C observed an active region on 2012 July 11 that exhibits several interesting features in the EUV line at 193 A. One of them is the existence of short, small brightenings "sparkling" at the edge of the active region; we call these EUV bright dots (EBDs). Individual EBDs have a characteristic duration of 25 s with a characteristic length of 680 km. These brightenings are not fully resolved by the SDO/AIA instrument at the same wavelength; however, they can be identified with respect to the Hi-C location of the EBDs. In addition, EBDs are seen in other chromospheric/coronal channels of SDO/AIA, which suggests a temperature between 0.5 and 1.5 MK. Based on t...
The second Hi-C flight (Hi-C2.1) provided unprecedentedly-high spatial and temporal resolution (∼... more The second Hi-C flight (Hi-C2.1) provided unprecedentedly-high spatial and temporal resolution (∼250km, 4.4s) coronal EUV images of Fe IX/X emission at 172Å, of AR 12712 on 29-May-2018, during 18:56:21-19:01:56 UT. Three morphologically-different types (I: dot-like, II: loop-like, III: surge/jetlike) of fine-scale sudden-brightening events (tiny microflares) are seen within and at the ends of an arch filament system in the core of the AR. Although type Is (not reported before) resemble IRIS-bombs (in size, and brightness wrt surroundings), our dot-like events are apparently much hotter, and shorter in span (70s). We complement the 5-minute-duration Hi-C2.1 data with SDO/HMI magnetograms, SDO/AIA EUV images, and IRIS UV spectra and slit-jaw images to examine, at the sites of these events, brightenings and flows in the transition-region and corona and evolution of magnetic flux in the photosphere. Most, if not all, of the events are seated at sites of opposite-polarity magnetic flux convergence (sometimes driven by adjacent flux emergence), implying likely flux cancellation at the microflare's polarity inversion line. In the IRIS spectra and images, we find confirming evidence of field-aligned outflow from brightenings at the ends of loops of the arch filament system. In types I and II the explosion is confined, while in type III the explosion is ejective and drives jet-like outflow. The light-curves from Hi-C, AIA and IRIS peak nearly simultaneously for many of these events and none of the events display a systematic cooling sequence as seen in typical coronal flares, suggesting that these tiny brightening-events have chromospheric/transition-region origin.
Symposium - International Astronomical Union, 1980
The soft x-ray (2–54 Å) pictures obtained by the S-054 experiment aboard SKYLAB provide an excell... more The soft x-ray (2–54 Å) pictures obtained by the S-054 experiment aboard SKYLAB provide an excellent opportunity to study the association of x-ray loop structures with radio bursts. We report here on the properties of meter-decameter wavelength radio bursts which appear to be associated with two different types of loop structures: a)Relatively short lived small scale loops, which are observed to link magnetic fields of opposite polarity, called x-ray bright points (XBPs); andb)Longer lived loop systems which appear to connect opposite magnetic polarities of an active region and active region complexes as well.
Soft X-ray images of the solar corona obtained during the last 20 years have systematically shown... more Soft X-ray images of the solar corona obtained during the last 20 years have systematically shown an intimate relationship between intense emitting structures and magnetic fields (Vaiana and Rosner 1978). The magnetic field confines a 106 K plasma, which is an intense source of soft X-ray photons. Therefore, it is natural to expect the bright X-ray structures to follow the field’s geometry. But this relationship does not seem to be just geometrical. It is generally believed that the energy necessary to heat the plasma comes from the dissipation of magnetic stresses, which are continually being re-generated by subphotospheric convective motions. However, there is still great uncertainty about the precise physical mechanisms involved in the production and release of the magnetic energy.
Proceedings of the International Astronomical Union, 2006
We present a statistical investigation of shear motion of the EUV footpoints in tworibbon solar f... more We present a statistical investigation of shear motion of the EUV footpoints in tworibbon solar flares, using the high spatial resolution data obtained in 1998-2005 by the Transition Region and Coronal Explorer (TRACE). In this study we have selected 50 well-observed X-and M-class two-ribbon flares. Our preliminary results are: a) 86% (43 out of 50) of these flares show shear change of footpoints and ribbon separation; b) there is no obvious ribbon separation in those 7 flares which have no shear change of the conjugate footpoints; c) in most events, the cessation of shear change is 0-2 minutes earlier than the end of the impulsive phase.
the Earth's force, needed to be taken into account from the start. In important ways, d' ... more the Earth's force, needed to be taken into account from the start. In important ways, d' Alembert was an inventive and insightful investigator in the areas of continuum mechanics and celestial mechanics, during the dozen or so years of his intense investment of himself in these studies. But he was a poor expositor, and his ideas also present intrinsic difficulties. Students seeking to assess his contributions to celestial mechanics must be immensely grateful to Dr ChaprontTouze for bringing the early memoirs into print and facilitating in innumerable ways our access to them.
Observations made with the Normal Incidence X-ray Telescope (NIXT) have shown that some X-ray emi... more Observations made with the Normal Incidence X-ray Telescope (NIXT) have shown that some X-ray emitting structures observed with NIXT resemble very closely the corresponding H-alpha plages. We have used hydrostatic models of coronal loops to explain such observations as strong emission from the lower section of high-pressure coronal arches.
Solar soft X-ray images taken simultaneously by the Yohkoh and the Normal Incidence X-ray Telesco... more Solar soft X-ray images taken simultaneously by the Yohkoh and the Normal Incidence X-ray Telescope (NIXT) reveal significantly different coronal structures. Coronal loops are more clearly seen in the Yohkoh images, and the isolated island-like structures seen in the NIXT image have been found to correspond to the footpoints of the Yohkoh loops. The difference is due to the difference in the temperature response of the telescopes: NIXT is sensitive to temperatures ranging from 0.9 to 3 MK, while Yohkoh is more sensitive to temperatures above 2.5 MK. The morphological differences reflect the multi-temperature (1-5 MK) nature of the solar coronal plasmas.
During the past year we have completed the changeover from the NIXT program to the new TXI soundi... more During the past year we have completed the changeover from the NIXT program to the new TXI sounding rocket program. The NIXT effort, aimed at evaluating the viability of the remaining portions of the NIXT hardware and design, has been finished and the portions of the NIXT which are viable and flightworthy, such as filters, mirror mounting hardware, electronics and telemetry interface systems, are now part of the new rocket payload. The backup NIXT multilayer-coated x-ray telescope and its mounting hardware have been completely fabricated and are being stored for possible future use in the TXI rocket. The H-alpha camera design is being utilized in the TXI program for real-time pointing verification and control via telemetry. A new H-alpha camera has been built, with a high-resolution RS170 CCD camera output. Two papers, summarizing scientific results from the NIXT rocket program, have been written and published this year: 1. "The Solar X-ray Corona," by L. Golub, Astrophysics and Space Science, 237, 33 (1996). 2. "Difficulties in Observing Coronal Structure," Keynote Paper, Proceedings STEPWG1 Workshop on Measurements and Analyses of the Solar 3D Magnetic Field, Solar Physics, 174, 99 (1997).
The postflight performance evaluation of the X-ray telescope was summarized. All payload systems ... more The postflight performance evaluation of the X-ray telescope was summarized. All payload systems and subsystems performed well within acceptable limits, with the sole exception of the light-blocking prefilters. Launch, flight and recovery were performed in a fully satisfactory manner. The payload was recovered in a timely manner and in excellent condition. The prefilter performance analysis showed that no X-ray images were detected on the processed flight film. Recommendations for improved performance are listed.
The coronal heating problem remains unsolved today, 80 years after its discovery, despite 50 year... more The coronal heating problem remains unsolved today, 80 years after its discovery, despite 50 years of suborbital and orbital coronal observatories. Tens of theoretical coronal heating mechanisms have been suggested, but only a few have been able to be ruled out. In this talk, we will explore the reasons for the slow progress and discuss the measurements that will be needed for potential breakthrough, including imaging the solar corona at small spatial scales, measuring the chromospheric magnetic fields, and detecting the presence of high temperature, low emission measure plasma. We will discuss three sounding rocket instruments developed to make these measurements: the High resolution Resolution Coronal Imager (Hi-C), the Chromospheric Lyman-Alpha Spectropolarimeter (CLASP), and the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS).
Uploads
Papers by Leon Golub